1. Field of the Invention
The invention relates to an annular gear that is used as a mechanism for transmitting power in various power transmission devices.
2. Description of the Related Art
Cited as one example of power transmission devices is a transmission mounted in a vehicle. In a transmission, a combination of various types of gears is used to transmit power, and a planetary gear unit is used in many cases. Gears that construct the planetary gear unit are a ring gear, a sun gear, and a pinion gear. As the ring gear, an annular gear with internal teeth is used. As the sun gear and a pinion gear, annular gears with external teeth are used.
Meanwhile, noise generated in the transmission has been a problem in the past, particularly gear noise. To address the problem, a transmission case is reinforced and vehicle sound insulation is strengthened. This, however, results in an increase in cost and weight. Further, countermeasures have not yet been taken for the aforementioned various types of annular gears from the standpoint of gear noise reduction.